1. Field of the Invention
This invention relates to a disk driving device and more particularly to a head feeding arrangement which is advantageous for the disk driving device.
2. Description of the Related Art
A stepping motor has heretofore been employed as a drive source for feeding a head in a disk driving device such as a floppy disk driving device. In performing a so-called seek action, the head is moved to a desired recording track on a disk by driving the stepping motor with driving pulses which are generated according to a step pulse signal supplied for moving the head from outside, for example, from a host computer or the like.
However, if the pulse interval, or a step rate, of the step pulse signal from the host computer becomes short, the stepping motor becomes incapable of following the step pulse signal any longer. In such a case, there arises an incident wherein the head fails to reach the desired track. Hereinafter this failure will be called a misseek. The misseek results from a build-up delay of the action of a mechanical part to be performed in response to the step pulse signal, due to static friction, inertia, mechanical backlash or play, etc., of a carriage on which the head is mounted, the stepping motor and a mechanism arranged to transmit the driving force of the stepping motor to the carriage.
During recent years, the disk driving device has become thinner in shape and compact in size. As a result, the size of the stepping motor also has become smaller. The driving force becomes smaller accordingly as the size of the stepping motor is reduced. The size of the mechanism for transmitting the driving force of the stepping motor to the carriage is also reduced for cost reduction. The reduction in size and cost has been disadvantageous in respect to accuracy and has brought about a tendency of increasing the build-up delay of the action mentioned above. The tendency becomes stronger depending on the environment particularly at a low ambient temperature. Further, in a case where the disk driving device is arranged to perform a driving action with a battery, the above-stated problem is apt to be brought about by a decrease in torque of the stepping motor resulting from a low voltage and battery consumption.
The above-stated misseek takes place sometimes for a step pulse signal of a step rate between 2.5 msec and 3 msec which is often adopted in manufactured products. The occurrence of such a misseek is undesirable with respect to reliability of recording or reproduction.
The reason why a build-up delay of the seek action causes a misseek in a case where the step rate is short is believed to be as follows. When the step pulse signal is supplied while the carriage, the stepping motor, etc., are quiescent, the stepping motor is not brought to an expected stable position by the excitation of the stepping motor driver in response to the first step pulse of the step pulse signal before a succeeding step pulse is supplied. In other words, the head has not been moved to a desired track when the succeeding step pulse is supplied. As a result, the excitation phase of the stepping motor driver is shifted by the succeeding, or second, step pulse while the stepping motor still remains in an unstable position. Under such a condition, the head cannot be moved to the desired track, thereby causing a misseek, because the torque of the stepping motor decreases to lower the speed of the head moving action, and the head is thus brought to a wrong place.